Susceptibility to rheumatoid arthritis (RA) is genetically linked to the HLA class II antigen known as DR4. Based on DNA sequence analysis, DR4 can be subdivided into several subtypes (eg. Dw4, Dw10, Dwl3, Dwl4, Dwl5) which differ from each other by only 1-4 amino acids. However, only some of these subtypes are associated with RA (ie. Dw4, Dw14, Dw15). Based on recent studies in mice which demonstrate that class II antigens can influence the T cell receptor (TCR) repertoire, it may be proposed that the differing association of DR4 subtypes with susceptibility to RA is due to their differing effects on the TCR repertoire. The overall goal of this project is to gain insight into the role of HLA class II antigens in determining the TCR repertoire. In particular, these studies will focus on the various subsets of DR4 and those DR1 and DR6 alleles which also display association with susceptibility to RA. The studies will include an analysis of the TCR repertoire of peripheral blood lymphocytes from selected individuals of known HLA type. The TCR repertoire will be analyzed by immunofluorescence using Vbeta-specific monoclonal antibodies and, quantitative PCR using Valpha and Vbeta-specific primers. In addition, studies will be performed to determine whether distinct TCR are used to recognize the different subtypes of DR4 and to define the characteristics that distinguish them. This will be accomplished by analyzing the TCR repertoire of a single individual in an alloreactive response to human B cells transfected with the various DR4 subtype alleles. Furthermore, the influence of HLA class II genes on selection of the TCR repertoire in responses to the DR4 subtypes will be assessed by determining how these repertoires vary with the HLA type of the responder.